[PATCH] gdb/testsuite: Fix set_unbuffered_mode.o handling in parallel mode

[Pedro Alves <pedro@palves.net>]

Cygwin/MinGW testing links in a set_unbuffered_mode.o object to all
test programs.  When running the testsuite in parallel mode, on
Cygwin, I noticed errors like:

  ERROR: remote_download to host of ..../build/set_unbuffered_mode.o to ..../build/set_unbuffered_mode_saved.o: cp: cannot open '..../build/set_unbuffered_mode.o' for reading: No such file or directory
...
  ERROR: remote_download to host of ..../build/set_unbuffered_mode.o to ..../build/set_unbuffered_mode_saved.o: cp: cannot stat '..../build/set_unbuffered_mode.o': No such file or directory
...
  ERROR: remote_download to host of ..../build/set_unbuffered_mode.o to ..../build/set_unbuffered_mode_saved.o: cp: skipping file '..../build/set_unbuffered_mode.o', as it was replaced while being copied

(Absolute paths elided above.)

The problem is that gdb_compile's unbuffered_mode_obj cache isn't
parallel safe.  This is fixed in this commit.

Change-Id: I67a289473c14ce0603d4b0beb755b124588f18d2
---
 gdb/testsuite/lib/gdb.exp | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index a0c4855ffc5..fbfa6f81b8f 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -5565,10 +5565,20 @@ proc gdb_compile {source dest type options} {
 	    #  which is time consuming, especially if we're remote
 	    #  host testing.
 	    #
+	    # Note the special care for GDB_PARALLEL.  In that
+	    # scenario, multiple expect instances will potentially try
+	    # to compile the object file at the same time.  The result
+	    # should be identical for every one of them, so we just
+	    # need to make sure that the final objfile is written to
+	    # atomically.
+
 	    if { $gdb_saved_set_unbuffered_mode_obj == "" } {
 		verbose "compiling gdb_saved_set_unbuffered_obj"
 		set unbuf_src ${srcdir}/lib/set_unbuffered_mode.c
-		set unbuf_obj ${objdir}/set_unbuffered_mode.o
+		# This gives us a per-expect-instance unique filename,
+		# which is important for GDB_PARALLEL.  See comments
+		# above.
+		set unbuf_obj [standard_temp_file set_unbuffered_mode.o]
 
 		set result [gdb_compile "${unbuf_src}" "${unbuf_obj}" object {nowarnings}]
 		if { $result != "" } {
@@ -5581,7 +5591,14 @@ proc gdb_compile {source dest type options} {
 		}
 		# Link a copy of the output object, because the
 		# original may be automatically deleted.
-		remote_download host $unbuf_obj $gdb_saved_set_unbuffered_mode_obj
+		if {[info exists ::GDB_PARALLEL]} {
+		    # Make sure to write the .o file atomically.
+		    # (Note GDB_PARALLEL mode does not support remote
+		    # host testing.)
+		    file rename -force -- $unbuf_obj $gdb_saved_set_unbuffered_mode_obj
+		} else {
+		    remote_download host $unbuf_obj $gdb_saved_set_unbuffered_mode_obj
+		}
 	    } else {
 		verbose "gdb_saved_set_unbuffered_obj already compiled"
 	    }

base-commit: c05dd51122c2d654031b04e02ad0ea5b53ffe5e2
-- 
2.43.2